Manufacturing method of electroluminescent device

ABSTRACT

An electroluminescent element which is superior in luminescence properties and lifetime can be provided by forming a thin film with high controllability according to the invention. An electroluminescent layer is formed over a first electrode by applying a current density of from 0.4 to 1.5 mA/cm 2  for from 0.8 to 3.0 seconds to a first electrode of the electroluminescent element in accordance with the fact that an electrolytic polymerization film can be formed over the surface of the electrode uniformly by keeping a current density and time for applying the current to the electrode within a predetermined range during electrolytic polymerization especially when the electrolytic polymerization film is required to be a thin film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for manufacturing anelectroluminescent element including an electroluminescent layer betweena pair of electrodes.

2. Related Art

An electroluminescent element includes an electroluminescent layerinterposed between a pair of electrodes (anode and cathode). Theemission mechanism is as follows. Upon applying a voltage between thepair of electrodes, holes injected from the anode and electrons injectedfrom the cathode are recombined with each other at luminescent centerswithin the electroluminescent layer to lead to formation of molecularexcitons, and the molecular excitons return to the ground state whileradiating energy to emit photon.

An electroluminescent layer in the electroluminescent element can beformed by a low molecular weight material or a high molecular weightmaterial by vapor deposition (including vacuum vapor deposition), spincoating, ink jetting, dipping, electrolytic polymerization, or the like.

These methods are appropriately selected depending on properties ofmaterials or a shape of a film. For example, electrolytic polymerizationis used to pattern form a film formed by high molecular weightmaterials. (For example, refer to Japanese Unexamined Patent PublicationNo. 9-97679.)

However, sufficient planarity of a deposited film is not availablethrough the conventional electrolytic polymerization at present.

By the fact that an electroluminescent layer used for anelectroluminescent element is formed to have a thickness ofapproximately from 1 to 100 nm, the planarity of the deposited filminfluences device characteristics of an electroluminescent element suchas luminescence properties or lifetime.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention toprovide an electroluminescent element which is superior in luminescenceproperties and lifetime by forming a thin film with highcontrollability.

The inventors found that a current applied to the surface of anelectrolytic polymerization film can be equalized by keeping currentdensity and time for applying a current to an electrode for electrolyticpolymerization within a predetermined range, consequently, theelectrolytic polymerization film can be deposited uniformly over thesurface of an electrode especially when the electrolytic polymerizationfilm is required to be formed into a thin film.

Therefore, a constituent feature of the invention is a method formanufacturing an electroluminescent element including a step of formingan electroluminescent layer between a pair of electrodes by anelectrochemical method, wherein the electroluminescent layer is formedin the condition that a current density of from 0.4 to 1.5 mA/cm² isapplied to a first electrode for from 0.8 to 3.0 seconds.

Moreover, in accordance with the fact that an electrolyticpolymerization film can be formed with high controllability especiallywhen the electrolytic polymerization film is formed to be thin, totalquantity of electrical charge per unit area of the first electrode iscontrolled in order to control the thickness of the electrolyticpolymerization film. Hence, according to the invention, the electrolyticpolymerization film is formed in the condition that total quantity ofelectrical charge per unit area of the first electrode is from 1.0 to1.2 mC/cm².

In the above each constituent feature, as an electroluminescent layerformed by the electrochemical method, a hole injecting layer, a holetransporting layer, a light-emitting layer, a hole blocking layer, or anelectron transporting layer can be formed. Above all, theelectrochemical method is suitable for the formation of the holeinjecting layer in forming a thin film with high controllability.

In the above each constituent feature, as a material for forming theelectroluminescent layer by an electrolytic polymerization, a compoundselected form the group consisting of pyrrol, indol, thiophene,3,4-ethylenedioxythiophene, benzene, naphthalene, azulene, and phenyleneoxide can be used.

In forming an electroluminescent layer by an electrolyticpolymerization, a thin film can be formed with high controllability bykeeping current density and time for polymerization within apredetermined range, consequently, an electroluminescent element whichis superior in device characteristics such as luminescence properties tothe conventional electroluminescent element.

These and other objects, features and advantages of the presentinvention will become more apparent upon reading of the followingdetailed description along with the accompanied drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are explanatory views for electrolytic polymerization;

FIG. 2 is an explanatory view for a device configuration of anelectroluminescent element;

FIG. 3 is an explanatory view for a device configuration of anelectroluminescent element;

FIG. 4 is a graph for showing relationship between current density and aarithmetic roughness average;

FIG. 5 is a graph for showing relationship between a arithmeticroughness average and current efficiency;

FIGS. 6A and 6B are explanatory views for showing an active matrixpanel;

FIG. 7 is an explanatory cross-sectional view for showing anelectroluminescent element connected to a TFT;

FIGS. 8A and 8B are explanatory views for showing a light-emittingdevice;

FIGS. 9A to 9G are explanatory views for showing electric appliances;

FIGS. 10A to 10D show AFM photographs showing surface states;

FIGS. 11A to 11D shows AFM photographs showing a surface state; and

FIG. 12 shows measurement results by SIMS for electroluminescent elementshown in FIG. 3.

DESCRIPTION OF THE INVENTION Embodiment Mode

A method for manufacturing an electroluminescent element according tothe present invention is explained with reference to FIGS. 1A and 1B inthis embodiment. Like components between FIGS. 1A and 1B are denoted bylike numerals.

According to the invention, a part of an electroluminescent layer isformed over an electrode (first electrode) 106 which is formed over asubstrate 105 by electrolytic polymerization using equipment asillustrated in FIG. 1A. As materials for the substrate 105, glass,quartz, transparent plastics, or the like can be used.

In addition, the first electrode 106 may serve as either an anode or acathode. A plurality of the first electrodes 106 may be pattern formedover the substrate 105.

In the case that the first electrode 106 serves as an anode, metalshaving large work functions (at least 4.0 eV), alloys, compounds havingelectrical conduction properties, and mixture of these materials can bepreferably used as anode materials. As specific examples of the anodematerials, ITO (indium tin oxide), IZO (indium zinc oxide) composed ofindium oxide mixed with zinc oxide (ZnO) of from 2 to 20%, aurum (Au),platinum (Pt), nickel (Ni), tungsten (W), chrome (Cr), molybdenum (Mo),ferrum (Fe), cobalt (Co), copper (Cu), palladium (Pd), nitride of metalmaterials (for example, TiN), or the like can be used.

In the case that the first electrode 106 serves as a cathode, metalshaving small work functions (at most 3.8 eV), alloys, compounds havingelectrical conduction properties, and mixture of these materials can bepreferably used as cathode materials. As specific examples of thecathode materials, a transition metal containing a rare earth metal canbe used, besides an element in the first or second periodic row, thatis, an alkaline metal such as Li, Cs, or the like, alkaline earth metalsuch as Mg, Ca, Sr, or the like, alloys of these elements (Mg:Ag,Al:Li), or compounds (LiF, CsF, CaF₂). Alternatively, the firstelectrode 106 can be formed by transition metal containing rare earthmetal and a lamination layer of the transition metal and metals such asAl, Ag, or ITO (including alloys).

The above anode and cathode materials are deposited by vapor depositionor sputtering to form a thin film. The thin film is preferably formed tohave a thickness of from 10 to 500 nm.

In the electroluminescent element according to the invention, in thecase that the first electrode 106 serves as an anode, the secondelectrode which is formed in later process serves as a cathode.

An electroluminescent element according to the invention has thestructure that light generated by recombination of carries within anelectroluminescent layer emits from either the first electrode 106 orthe second electrode, or both of the electrodes. When light emits fromthe first electrode 106, the first electrode 106 is formed by materialshaving light transmission properties. When light emits from the secondelectrode, the second electrode is formed by a material having lighttransmission properties. The case that the first electrode 106 serves asan anode formed by materials having light transmission properties andthe second electrode serves as a cathode formed by materials havinglight shielding properties is explained in this embodiment.

As shown in FIG. 1A, a reaction tank 101 holds electrolytic solution102, and the electrolytic solution 102 is provided with a substrate 105having the first electrode 106 electrically connected to a power source104 via a wiring 103, a counter electrode 107, and a reference electrode108. In addition, the substrate 105 is secured by a support medium 109which connects electrically the first electrode 106 to the wiring 103.

The power source 104 includes a potentiostat which is capable ofapplying a constant electric potential and a coulombmeter which measuresan amount of a flowing electric charge. The counter electrode 107 isformed by platinum. Further, the reference electrode 108 is formed byAg/AgCl.

The reaction tank 101 is provided over a magnetic stirrer 110. In thereaction tank 110, a rotator 111 in the electrolytic solution 102 iscontrolled by the magnetic stirrer 110 to stir continuously theelectrolytic solution 102.

When a predetermined current is applied to the counter electrode 107,and the first electrode 106 over the substrate 105 via the supportmedium 109, respectively, monomer or oligomer in the electrolyticsolution 102 are polymerized on the surface of the first electrode 106by electrolytic polymerization to form a first electroluminescent layer(electrolytic polymerization film) 112 containing polymer as its maincomponents. According to the invention, an electrolytic polymerizationfilm with surface roughness of at most 6.0 nm, preferably, from 4.0 to5.0 nm can be formed by setting the condition, that is, the firstelectrode 106 used has the size of 0.04 cm², the current is applied fromthe power source 104 at from 0.016 to 0.06 mA, and the current isapplied for from 0.8 to 3.0 sec. Consequently, decline in luminousefficiency or deterioration of an electroluminescent element due toelectric voltage concentration which becomes a problem caused by poorplanarity of a film surface can be prevented, and device characteristicsand lifetime can be improved.

In the invention, as a supporting electrolyte contained in theelectrolytic solution 102, salts such as natrium perchlorate, lithiumperchlorate, tetrabutylammonium perchlorate (hereinafter, TBAP), ortetrabutylammonium tetrafluoroborate; another bases; or acids can beused. The solvent for the electrolytic solution 102 can be selected fromthe group consisting of water, acetonitrile, benzonitrile,N,N-dimethylformamide, dichloromethane, tetrahydrofuran, propionecarbonate; or mixed solvent of a plurality kinds of the solvents can beused.

As monomer or oligomer contained in the electrolytic solution 102,aniline, phenylene oxide, or the like can be used in addition tothiophene based materials (specifically, thiophene,3,4-ethylenedioxythiophene, or the like), pyrrol based materials(specifically, pyrrol, indol, or the like), or aromatic hydrocarbonbased materials (specifically, benzene, naphthalene, azulene, or thelike).

A second electroluminescent layer 113 is formed over a firstelectroluminescent layer 112. In the invention, in the case that thefirst electroluminescent layer 112 is formed by a single layer which canemit light (the first electroluminescent layer 112 includes alight-emitting layer), a second electrode can be formed over the firstelectroluminescent layer 112. In this embodiment, the case that thesecond electroluminescent layer (including a light-emitting layer) isstacked over the first electroluminescent layer 112 (not including alight-emitting layer) formed by an electrolytic polymerization film isexplained with reference to FIG. 2.

In this embodiment, the first electroluminescent layer 112 is a holeinjecting layer, and the second electroluminescent layer 113 can beformed by a single layer or a lamination layer including at least alight-emitting layer. In case of forming a lamination layer, a holetransporting layer, a hole blocking layer, an electron transportinglayer, or the like can be formed besides the light-emitting layer byvapor deposition, coating, ink jetting, or the like.

In the case that the first electroluminescent layer 112 formed by anelectrolytic polymerization film forms an hole injecting layer, aniline,phenylene oxide, or the like can be used in addition to thiophene basedmaterials or pyrrol based materials such as thiophene,3,4-ethylenedioxythiophene, pyrrol, or indol can be used as monomer oroligomer.

In the case that a hole transporting layer is included in the secondelectroluminescent layer 113, aromatic amine (that is, the one having abenzene ring-nitrogen bond) compounds are preferably used as holetransportation materials. For example, besides4,4′-bis[N-(3-methylphenyl)-N-phenyl-amino]-biphenyl (hereinafter, TPD),derivatives thereof such as4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (hereafter, a-NPD) iswidely used. Also used are star burst aromatic amine compounds,including 4,4′,4″-tris(N,N-diphenyl-amino)-triphenyl amine (hereafter,TDATA), and 4,4′,4″-tris[N-(3-methylphenyl)-N-phenyl-amino]-triphenylamine (hereafter, MTDATA).

As light-emitting materials for forming the light-emitting layerincluded in the second electroluminescent layer 113, in specific,various-fluorescent dyes are useful, besides metal complexes such astris(8-quinolinolate)aluminum (hereinafter, Alq₃),tris(4-methyl-8-quinolinolate)aluminum (hereinafter, Almq₃),bis(10-hydroxybenzo[h]-quinolinato)beryllium (hereinafter, BeBq₂),bis(2-methyl-8-quinolinolate)-(4-hydroxy-biphenylyl)-aluminum(hereinafter, BAlq), bis[2-(2-hydroxyphenyl)-benzooxazolate]zinc(hereinafter, Zn(BOX)₂), andbis[2-(2-hydroxyphenyl)-benzothiazolate]zinc (hereinafter, Zn(BTZ)₂).Additionally, a triplet luminescent material containing mainly complexeswith platinum or iridium as central metals can be used. As a tripletluminescent material, tris(2-phenylpyridine)iridium (hereinafter,Ir(ppy)₃), 2,3,7,8,12,13,17,18-octaethyl-21H, 23H-porphyrin-platinum(hereinafter, PtOEP), or the like can be used.

In the case that a hole blocking layer is included in the secondelectroluminescent layer 113, Balq,1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene (hereafter,OXD-7), triazole derivatives such as3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole(hereafter, TAZ) and3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(hereafter, p-EtTAZ), bathophenanthroline (hereafter, BPhen), andbathocuproin (hereafter, BCP) can be used as hole blocking materials.

In the case that an electron transporting layer is included in thesecond electroluminescent layer 113, metal complexes having a quinolineskeleton or benzoquinoline skeleton, such as the aforementioned Alq₃,Almq₃, BeBq₂; and mixed ligand complexes such as BAlq₂ are useful aselectron transporting materials. In addition, metal complexes havingoxazole-based and thiazole-based ligands such as Zn(BOX)₂ and Zn(BTZ)₂can be used. Further, oxadiazole derivatives such as2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (hereafter, PBD),and OXD-7, triazole derivatives such as TAZ and p-EtTAZ, phenanthrolinederivatives such as bathophenanthroline (BPhen), and bathocuproin (BCP)can be used.

Then, a second electrode 114 serving as a cathode is formed over thesecond electroluminescent layer 113. As cathode materials for the secondelectrode 114, above described materials may be used.

Accordingly, an electroluminescent element including anelectroluminescent layer formed between a pair of electrodes byelectrolytic polymerization can be manufactured.

EXAMPLE 1

In this example, an electroluminescent element using an electrolyticpolymerization film formed by electrolytic polymerization as anelectroluminescent layer will be explained with reference to FIG. 3.

A first electrode 301 is formed by ITO over a substrate 300. The area ofthe first electrode 301 according to this example is 2×2 mm².

Then, a first electroluminescent layer 302 is formed over the firstelectrode 301 by electrolytic polymerization explained with reference toFIG. 1A. Further, electrolytic solution in a reaction tank containsthiophene of 10 mM as monomer, acetonitrile as a solvent, and TBAP of0.1 M as a supporting electrolyte.

The substrate 300 is secured by a supporting medium, then, soaked andimmersed in the electrolytic solution. Next, a first electroluminescentlayer 302 is formed over the first electrode 301 by applying apredetermined current from the power source for predetermined time. Thearea of the first electrode 301 according to this example is 2×2 mm².Considering that the thickness of a film formed by electrolyticpolymerization depends on the total quantity of electric charge per unitarea (mC/cm²), time for applying a current is controlled so that thetotal quantity of electrical charge per unit area is 1.2 mC/cm².Consequently, the first electroluminescent layer 302 is formed by anelectrolytic polymerization film (PEDOT: poly(3,4-ethylenedioxythiophene) to serve as a hole injecting layer 311.

Drying treatment for the substrate can be carried out according to thefollowing procedure. The first electroluminescent layer 302 is formed,the substrate is taken together with the supporting medium out of theelectrolytic solution, and the substrate is dried at a temperature offrom room temperature to 150° C. in vacuo. According to this example,the substrate is dried at a temperature of 110° C.

Then, a second electroluminescent layer 303 is formed over the firstelectroluminescent layer 302. According to this example, the secondelectroluminescent layer 303 is formed to have a lamination layercomprising a hole transporting layer 312 and a light-emitting layer 313by vapor deposition.

The substrate 300 provided with the first electroluminescent layer 302is secured with a substrate holder of a commercial vacuum depositionequipment in such a way that the surface provided with the firstelectroluminescent layer 302 is down. Then, α-NPD is put into anevaporation source installed in the internal of the vacuum depositionequipment. And then, the hole transporting layer 312 is formed to have athickness of 30 nm by vapor deposition with a resistive heating method.

Next, a light-emitting layer 313 is formed. Within the light-emittinglayer 313, holes and electrons are recombined with each other to emitlight. Here, Alq₃ is deposited to have a thickness of 50 nm inaccordance with the same procedure conducted for forming the holetransporting layer 312.

After stacking the first electroluminescent layer 302 and the secondelectroluminescent layer 303, a second electrode 304 is formed to serveas a cathode by vapor deposition or sputtering. According to thisembodiment, the second electrode 304 is formed to have a laminationstructure by depositing calcium fluoride (CaF) to have a thickness of 2nm by vapor deposition over the second electroluminescent layer 303, andaluminum (Al) is deposited to have a thickness of 100 nm by vapordeposition thereon.

For examining variation of planarity of the surface according to changeof current density during forming the first electroluminescent layer 302by electrolytic polymerization, surface observation of the firstelectroluminescent layer 302 was carried out by Atomic Force Microscope(AFM). Table 1 shows the measurement conditions. FIGS. 10A to 10D and11A to 11D show the measurement results. In FIGS. 10A to 10D and 11A to11D, 10A shows the surface state of the first electrode 301 formed byITO, and 10B to 11D show the surface state of the firstelectroluminescent layer 302 formed in accordance with the conditions ofcurrent density and time for applying a current as shown in Table 1.

TABLE 1 Measurement condition 10A 10B 10C 10D 11A 11B 11C 11D Currentdensity — 0.05 0.10 0.40 0.60 1.00 1.50 2.00 (mA/cm²) — 24.0 12.0 3.02.0 1.2 0.8 0.6 Time (sec.)

FIG. 4 shows the planarity of a film surface obtained from the surfaceobservation shown in FIGS. 10A to 10D and 11A to 11D. The planarity of afilm surface is described by a arithmetic roughness average (Ra). Inaddition, the term as used herein “arithmetic roughness average” refersto centerline roughness which is extended to three dimensions forapplying roughness of the surface of a film. The centerline roughness isdefined by JIS B0601.

As shown in FIG. 4, the horizontal axis represents a current density perunit area, which is converted from current value applied from a powersource during electrolytic polymerization, and the vertical axisrepresents an arithmetic roughness average of the surface of a depositedfilm.

The results show that an arithmetic roughness average (Ra) can bereduced especially when the current density falls within the range of0.4 to 1.5 mA/cm² and the time for applying a current falls within therange of 0.8 to 3.0 sec. Consequently, a film which has excellentplanarity can be formed.

Further, a second electroluminescent layer and a second electrode areformed over the first electroluminescent layer formed in the sameconditions as those shown in FIG. 4 to have the same deviceconfiguration as that shown in FIG. 3. Then, device characteristics ofthe obtained electroluminescent element were measured. FIG. 5 shows themeasurement results. The device characteristics of theelectroluminescent element are described by a current efficiency (cd/A).

In FIG. 5, the horizontal axis represents current density applied to afirst electrode during electrolytic polymerization, the left sidevertical axis represents an arithmetic roughness average of a filmsurface of a first electroluminescent layer formed by electrolyticpolymerization, and the right side vertical axis represents currentefficiency of the electroluminescent element. Also in this case, thearea of the electrode is 2×2 mm², and current density and time forapplying a current were controlled so that total quantity of electricalcharge is 1.2 mC/cm². Therefore, the measurement results of anarithmetic roughness average (Ra) and current efficiency are shown inthe case that the electroluminescent element is formed in the conditionsthat the current density is applied at 0.20, 0.4, and 0.6 mA/cm² for 6,3, and 2 sec., respectively.

With respect to the current density, an arithmetic roughness average,and current efficiency, the results show that current efficiency wasimproved by reducing an arithmetic roughness average by controllingcurrent density. The results shown in FIGS. 4 and 5 show that anarithmetic roughness average (Ra) can be reduced especially when thecurrent density falls within the range of from 0.4 to 1.5 mA/cm² and thetime for applying a current falls within the range of from 0.8 to 3.0sec. Consequently, an arithmetic roughness average (Ra) can be reduced,and current efficiency can be improved.

Secondary Ion Mass Spectrometry (SIMS) was carried out focusing on Satoms contained in thiophene. Here, the electroluminescent element shownin FIG. 3 was used as a sample. Primary ions (Cs+) were irradiated inthe sample from the side of the second electrode. As shown in FIG. 12,the peak of secondary ion intensity of S was occurred in the regionwhere secondary ion intensity of C+N, C, and H was decreased drasticallyand secondary ion intensity of In+O was increased drastically.Therefore, the formation of a first electroluminescent layer by anelectrolytic polymerization was recognized over a first electrodecontaining In. SIMS used here was carried out as the followingprocedure, that is, an ion beam was emitted to the surface of a solidsample in vacuo, and ejected secondary ions (constituent atoms of thesample) from the sample were sorted on the basis of mass-to-chargeratio, then, mass spectrometry was carried out.

EXAMPLE 2

In this example, an active matrix panel in which a driver circuit unitand a pixel portion are formed over one substrate and a plurality ofelectroluminescent elements having electroluminescent layers formed byelectrolytic polymerization is formed in the pixel portion will beexplained with reference to FIGS. 6A, 6B and 7.

As shown in FIG. 6A, a source side driver circuit 602, a gate sidedriver circuit 603, which are included in a driver circuit unit, and apixel portion 604 are formed over a substrate 601. Signal lines 605,scanning lines 606, and current supply lines 607 are formed over a pixelportion 604. In addition, the source side driver circuit 602 and thegate side driver circuit 603 are connected to the outside via leadwirings 608. Further, the current supply lines 607 are also connected tothe outside via the lead wirings 608.

The lead wirings 608 can connect electrically to the outside byconnecting to an FPC 610 in a connection portion 609.

FIG. 6B is an enlarged view showing the pixel portion 604. In the pixelportion 604, a plurality of first electrodes 611 including a pluralityof pixels is formed. Though not shown, the first electrodes 611 connectelectrically to TFTs formed previously over a substrate via wirings.

The signal lines 605, the scanning lines 606, and the current supplylines 607 are formed in the periphery of the first electrodes 611. Aninsulating layer 612 formed over the pixel portion 604 covers the signallines 605, the scanning lines 606, and the current supply lines 607except the first electrodes 611.

According to this embodiment, a predetermined current is applied from apower source to the first electrodes 611 formed over a panel via the FPC610 to carry out electrolytic polymerization for forming the firstelectroluminescent layer which is a part of an electroluminescent layerover the first electrode. The electrolytic polymerization can be carriedout in accordance with the same procedure explained in Embodiment withthe equipment illustrated in FIG. 1A.

A panel according to this embodiment has diagonal conjugate diameter of1.89 inches, a pixel portion has the size of 11.56 cm², the number ofpixels is 176×3×184, the first electrodes 611 which are exposed formedin each pixel has the size of 5412 μm². Here, since the firstelectroluminescent layer is formed simultaneously over all of the firstelectrodes 611, the area of the electrode is 5.26 cm².

Further, electrolytic solution in a reaction tank contains thiophene of10 mM as monomer, acetonitrile as a solvent, and TBAP of 0.1 M as asupporting electrolyte.

According to this example, an-electrolytic polymerization film servingas a first electroluminescent layer can be formed by applying a currentof 3.156 mA for two seconds.

After forming the electrolytic polymerization film, the substrate istaken together with a support medium from electrolytic solution anddried at 110° C. in vacuo.

After forming the first electroluminescent layer over the firstelectrode 611 as described above, an electroluminescent element as shownin FIG. 7 can be formed by stacking another layer over the firstelectroluminescent layer. Further, the electroluminescent element canalso be formed as the following manner, that is, the FPC shown in FIG.6A is detached from the substrate after forming the firstelectroluminescent layer, and subsequent processes are carried out. FIG.7 shows a part of the cross-sectional structure of a pixel formed in thepixel portion shown in FIG. 6B.

The first electrode 611 is electrically connected to a TFT 620comprising a source region 614, a drain region 615, a channel formationregion 616, a gate insulating film 617, and a gate electrode 618 via awiring 619. The TFT 620 and the edges of the first electrode 611 arecovered by the insulating layer 612.

A second electroluminescent layer 622 is formed over a firstelectroluminescent layer 613. The second electroluminescent layer 622according to this example is formed to have a lamination structure of ahole transporting layer and a light-emitting layer by vapor deposition,which is similar to that in Example 1.

An electroluminescent element 624 is formed by forming a secondelectrode 623 over the second electroluminescent layer 622.

By practicing this example, a panel which has a driver circuit unit anda pixel portion over one substrate, and which has an electroluminescentlayer formed by electrolytic polymerization according to the inventioncan be manufactured.

EXAMPLE 3

In this example, a light-emitting device having an electroluminescentelement according to the present invention in a pixel portion will beexplained with reference to FIGS. 8A and 8B. FIG. 8A is a top view of alight-emitting device. FIG. 8B is a cross-sectional view of FIG. 8Ataken along the line A–A′. Reference numeral 801 by a dotted linedenotes a source side driver circuit; reference numeral 802 denotes apixel portion; 803, a gate side driver circuit; 804, a sealingsubstrate; and 805, sealing agent. The inside portion surrounded by thesealing agent 805 is space 807.

Reference 808 denotes a lead wiring for transmitting signals inputted tothe source signal line driver circuit 801 and the gate signal linedriver circuit 803. The lead wiring receives video signals, clocksignals, start signals, or reset signals from an FPC (flexible printedcircuit) 809 serving as an external input terminal. Although only FPC isillustrated in the drawing, a PWB (printed wirings board) may beattached to the FPC. As used in this specification, the term“light-emitting device” refers not to only a main body of alight-emitting device but also to the main body provided with the FPC809 or PWB.

Then, a cross-sectional structure will be explained with reference toFIG. 8B. A driver circuit and a pixel portion are formed over asubstrate 810. In FIG. 8B, the source side driver circuit 801 as adriver circuit unit and the pixel portion 802 are illustrated.

The source signal line driver circuit 801 is provided with a CMOScircuit formed by combining an n-channel TFT 823 and a p-channel TFT824. A TFT for forming a driver circuit may be formed by a known CMOS,PMOS, or NMOS circuit. In this example, a driver integrated type inwhich a driver circuit is formed over a substrate is described, but notexclusively, the driver circuit can be formed outside instead of over asubstrate.

The pixel portion 802 includes a plurality of pixels including aswitching TFT 811, a current control TFT 812, and a first electrode 813connected electrically to the drain of the current control TFT 812.Further, an insulator 814 is formed to cover the edge of the firstelectrode 813. Here, the insulator 814 is formed by a positive typephotosensitive acrylic resin film.

In order to make favorable coverage, an upper edge portion and a loweredge portion of the insulator 814 are formed to have a curved facehaving a radius of curvature. For example, positive type photosensitiveacrylic is used as a material for the insulator 814, only upper edgeportion of the insulator 814 is preferably having a radius of curvature(from 0.2 to 3 μm). As the insulator 814, either a negative typephotosensitive resin that becomes insoluble to etchant by light or apositive type photosensitive resin that becomes dissoluble to etchant bylight can be used.

An electroluminescent layer 816 and a second electrode 817 are formedover the first electrode 813, respectively. As a material for the firstelectrode 813 serving as an anode, a material having a large workfunction is preferably used. For instance, the first electrode can beformed by a single layer such as an ITO (indium tin oxide) film, an IZO(indium zinc oxide) film, a titanium nitride film, a chromic film, atungsten film, a Zn film, or a Pt film; a lamination layer including afilm containing mainly titanium nitride and a film containing mainlyaluminum; a three lamination layer including a titanium nitride film, afilm containing aluminum as its main component, and a titanium nitride;or the like. In case of adopting the lamination layer, the firstelectrode can be formed to have a low resistance as a wiring, and makegood ohmic contact, and serve as an anode.

The electroluminescent layer 816 is formed by electrolyticpolymerization according to the invention. In case of forming theelectroluminescent layer 816 to have a lamination structure, anelectroluminescent layer formed by electrolytic polymerization andanother electroluminescent layer formed by another method can bestacked. As another method for forming the electroluminescent layer,vapor deposition using an evaporation mask, coating, or ink jetting canbe used.

Among the electroluminescent layers 816, the film formed by electrolyticpolymerization is formed by oligomer or polymer. A film formed byanother method may be formed by either low molecular weight materials orhigh molecular weight materials. In addition, an electroluminescentlayer can be partly formed by an inorganic compound as well as anorganic compound.

As a material for the second electrode (cathode) 817 formed over theelectroluminescent layer 816, a material having a small work function(Al, Ag, Li, Ca, alloys of these elements such as MgAg, MgIn, AlLi, orinorganic materials CaF₂, or CaN) can be used. In case that lightgenerated from the electroluminescent layer 816 pass through the secondelectrode (cathode) 817, the second electrode (cathode) 817 ispreferably formed by a lamination layer including a thin metal film anda transparent conductive film (alloys such as indium tin oxide (ITO),indium zinc oxide (In₂O₃—ZnO), zinc oxide (ZnO), or the like).

The sealing substrate 804 is pasted onto the substrate 810 with thesealing agent 805 to encapsulate an electroluminescent element 818within the space 807 surrounded by the substrate 810, the sealingsubstrate 804, and the sealing agent 805. The invention comprehends notonly the case that the space 807 is filled with inert gases (such asnitrogen or argon) but also the case that the space 807 is filled withthe sealing agent 805.

The sealing agent 805 is preferably formed by epoxy-based resin. Inaddition, it is desirable that the material for the sealing agentinhibits the penetration of moisture or oxygen as much as possible. As amaterial for the sealing substrate 804, a plastic substrate such as FRP(fiberglass-reinforced plastics), PVF (polyvinyl fluoride), polyester,or acrylic can be used besides a glass substrate or a quartz substrate.

Accordingly, a light-emitting device having an electroluminescentelement according to the invention can be obtained.

The light-emitting device described in this example can be practiced bycombining freely with the configuration of the electroluminescentelement explained in Examples 1 and 2.

EXAMPLE 4

Various electric appliances completed by using a light-emitting devicehaving an electroluminescent element according to the present inventionwill be explained in this example.

Given as examples of such electric appliances manufactured by using thelight-emitting device having the electroluminescent element according tothe invention: a video camera, a digital camera, a goggles-type display(head mount display), a navigation system, a sound reproduction device(a car audio equipment, an audio set and the like), a laptop personalcomputer, a game machine, a portable information terminal (a mobilecomputer, a cellular phone, a portable game machine, an electronic book,or the like), an image reproduction device including a recording medium(more specifically, a device which can reproduce a recording medium suchas a digital versatile disc (DVD) and so forth, and includes a displayfor displaying the reproduced image), or the like. FIGS. 9A to 9G showvarious specific examples of such electric appliances.

FIG. 9A illustrates a display device which includes a casing 2001, asupport table 2002, a display portion 2003, a speaker portion 2004, avideo input terminal 2005, or the like. The light-emitting device havingthe electroluminescent element according to the invention can be usedfor the display portion 2003. The display device is including all of thedisplay devices for displaying information, such as a personal computer,a receiver of TV broadcasting, an advertising display, and the like.

FIG. 9B illustrates a laptop computer which includes a main body 2201, acasing 2202, a display portion 2203, a keyboard 2204, an externalconnection port 2205, a pointing mouse 2206, or the like. Thelight-emitting device having the electroluminescent element according tothe invention can be used to the display portion 2203.

FIG. 9C illustrates a mobile computer which includes a main body 2301, adisplay portion 2302, a switch 2303, an operation key 2304, an infraredport 2305, or the like. The light-emitting device having theelectroluminescent element according to the invention can be used to thedisplay portion 2302.

FIG. 9D illustrates an image reproduction device including a recordingmedium (more specifically, a DVD reproduction device), which includes amain body 2401, a casing 2402, a display portion A 2403, another displayportion B 2404, a recording medium (DVD or the like) reading portion2405, an operation key 2406, a speaker portion 2407, or the like. Thedisplay portion A 2403 is used mainly for displaying image information,while the display portion B 2404 is used mainly for displaying characterinformation. The light-emitting device having the electroluminescentelement according to the invention can be used to the display potion A2403 and the display portion B 2404. Note that the image reproductiondevice with a recording medium further includes a domestic game machineor the like.

FIG. 9E illustrates a goggle type display (head mounted display), whichincludes a main body 2501, a display portion 2502, and an arm portion2503. The light-emitting device having the electroluminescent elementaccording to the invention can be used to the display portion 2502.

FIG. 9F illustrates a video camera which includes a main body 2601, adisplay portion 2602, a casing 2603, an external connecting port 2604, aremote control receiving portion 2605, an image receiving portion 2606,a battery 2607, a sound input portion 2608, an operation key 2609, aneyepiece potion 2610, or the like. The light-emitting device having theelectroluminescent element according to the invention can be used to thedisplay portion 2602.

FIG. 9G illustrates a cellular phone which includes a main body 2701, acasing 2702, a display portion 2703, a sound input portion 2704, a soundoutput portion 2705, an operation key 2706, an external connecting port2707, an antenna 2708, or the like. The light-emitting device having theelectroluminescent element according to the invention can be used to thedisplay portion 2703.

As set forth above, the light-emitting device having theelectroluminescent element according to the invention can be appliedvariously to a wide range of electric appliances in all fields. Byapplying the light-emitting device to various fields' electricappliances, low power consumption and long lifetime can be achieved.

Although the present invention has been fully described by way ofexamples with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless otherwise such changes andmodifications depart from the scope of the present invention hereinafterdescribed, they should be construed as being included therein.

1. A method for manufacturing an electroluminescent device comprising astep of forming an electroluminescent layer between a pair of electrodesin the electroluminescent device, wherein the electroluminescent layeris formed using an electrochemical method by flowing a current to one ofthe pair of electrodes with a current density from 0.4 to 1.5 mA/cm² for0.8 to 3.0 seconds.
 2. A method for manufacturing an electroluminescentdevice according to claim 1, wherein the electroluminescent layercomprises a compound selected from the group consisting of pyrrol,indol, thiophene, 3,4-ethylenedioxythiophene, benzene, naphthalene,azulene, and phenylene oxide.
 3. A method for manufacturing an electricappliance having the electroluminescent device according to claim 1,wherein the electric appliance is selected from the group consisting ofa display device, a laptop computer, a mobile computer, an imagereproduction device, a goggle type display, a video camera and acellular phone.
 4. A method for manufacturing an electroluminescentdevice comprising a step of forming an electroluminescent layer betweena pair of electrodes in the electroluminescent device, wherein theelectroluminescent layer is formed using an electrochemical method byflowing a current with a current density from 0.4 to 1.5 mA/cm² to oneof the pair of electrodes for 0.8 to 3.0 seconds, and wherein totalquantity of electrical charge per unit area of the one of the pair ofelectrodes is from 1.0 to 1.2 mC/cm² in the electrochemical method.
 5. Amethod for manufacturing an electroluminescent device according to claim4, wherein the electroluminescent layer comprises a compound selectedfrom the group consisting of pyrrol, indol, thiophene,3,4-ethylenedioxythiophene, benzene, naphthalene, azulene, and phenyleneoxide.
 6. A method for manufacturing an electric appliance having theelectroluminescent device according to claim 4, wherein the electricappliance is selected from the group consisting of a display device, alaptop computer, a mobile computer, an image reproduction device, agoggle type display, a video camera and a cellular phone.
 7. A methodfor manufacturing an electroluminescent device comprising a step offorming an electroluminescent layer between a pair of electrodes in theelectroluminescent device, wherein the electroluminescent layer has alamination structure comprising a first electroluminescent layer and asecond electroluminescent layer, wherein the first electroluminescentlayer is formed using an electrochemical method by flowing a current toone of the pair of electrodes with a current density from 0.4 to 1.5mA/cm² for 0.8 to 3.0 seconds; and wherein the second electroluminescentlayer is formed by vapor deposition.
 8. A method for manufacturing anelectroluminescent device according to claim 7, wherein the firstelectroluminescent layer comprises a compound selected from the groupconsisting of pyrrol, indol, thiophene, 3,4-ethylenedioxythiophene,benzene, naphthalene, azulene, and phenylene oxide.
 9. A method formanufacturing an electric appliance having the electroluminescent deviceaccording to claim 7, wherein the electric appliance is selected fromthe group consisting of a display device, a laptop computer, a mobilecomputer, an image reproduction device, a goggle type display, a videocamera and a cellular phone.
 10. A method for manufacturing anelectroluminescent device comprising a step of forming anelectroluminescent layer between a pair of electrodes in theelectroluminescent device, wherein the electroluminescent layer has alamination structure comprising a first electroluminescent layer and asecond electroluminescnet layer, wherein the first electroluminescentlayer is formed using an electrochemical method by flowing a current toone of the pair of electrodes with a current density from 0.4 to 1.5mA/cm² for 0.8 to 3.0 seconds, wherein total quantity of electricalcharge per unit area of the one of the pair of electrodes is from 1.0 to1.2 mC/cm² in the electrochemical method, and wherein the secondelectroluminescent layer is formed by vapor deposition.
 11. A method formanufacturing an electroluminescent device according to claim 10,wherein the first electroluminescent layer comprises a compound selectedfrom the group consisting of pyrrol, indol, thiophene,3,4-ethylenedioxythiophene, benzene, naphthalene, azulene, and phenyleneoxide.
 12. A method for manufacturing an electric appliance having theelectroluminescent device according to claim 10, wherein the electricappliance is selected from the group consisting of a display device, alaptop computer, a mobile computer, an image reproduction device, agoggle type display, a video camera and a cellular phone.
 13. A methodfor manufacturing an electroluminescent device comprising a step offorming an electroluminescent layer between a pair of electrodes in theelectroluminescent device, wherein the electroluminescence layercomprises: a hole injecting layer; a hole transporting layer; and alight-emitting layer, wherein the hole injecting layer is formed usingan electrochemical method by flowing a current to one of the pair ofelectrodes with a current density from 0.4 to 1.5 mA/cm² for 0.8 to 3.0seconds, and wherein the hole transporting layer and the light-emittinglayer are formed by vapor deposition.
 14. A method for manufacturing anelectroluminescent device according to claim 13, wherein the holeinjecting layer comprises a compound selected from the group consistingof pyrrol, indol, thiophene, 3,4-ethylenedioxythiophene, benzene,naphthalene, azulene, and phenylene oxide.
 15. A method formanufacturing an electric appliance having the electroluminescent deviceaccording to claim 13, wherein the electric appliance is selected fromthe group consisting of a display device, a laptop computer, a mobilecomputer, an image reproduction device, a goggle type display, a videocamera and a cellular phone.
 16. A method for manufacturing anelectroluminescent device comprising a step of forming anelectroluminescent layer between a pair of electrodes in theelectroluminescent device, wherein the electroluminescent layercomprises: a hole injecting layer; a hole transporting layer; and alight-emitting layer, wherein the hole injecting layer is formed usingan electrochemical method by flowing a current to one of the pair ofelectrodes with a current density from 0.4 to 1.5 mA/cm² for 0.8 to 3.0seconds, wherein total quantity of electrical charge per unit area ofthe one of the pair of electrodes is from 1.0 to 1.2 mC/cm² in theelectrochemical method, and wherein the hole transporting layer and thelight-emitting layer are formed by vapor deposition.
 17. A method formanufacturing an electroluminescent device according to claim 16,wherein the hole injecting layer comprises a compound selected from thegroup consisting of pyrrol, indol, thiophene,3,4-ethylenedioxythiophene, benzene, naphthalene, azulene, and phenyleneoxide.
 18. A method for manufacturing an electric appliance having theelectroluminescent device according to claim 8, wherein the electricappliance is selected from the group consisting of a display device, alaptop computer, a mobile computer, an image reproduction device, agoggle type display, a video camera and a cellular phone.
 19. A methodfor manufacturing a semiconductor device comprising a step of forming anorganic layer on an electrode of the semiconductor device, wherein theorganic layer is formed using an electrochemical method by flowing acurrent to the electrode with a current density from 0.4 to 1.5 mA/cm²for 0.8 to 3.0 seconds.
 20. A method according to claim 19, whereintotal quantity of electrical charge per unit area of the electrode isfrom 1.0 to 1.2 mC/cm² in the electrochemical method.
 21. A methodaccording to claim 19, further comprising a step of forming a secondorganic layer over the first organic layer by vapor deposition.
 22. Amethod according to claim 21, wherein the second organic layer is a holeinjecting layer.